Powering tyrosol antioxidant capacity and osteogenic activity by biocatalytic polymerization

Oxidative polymerization of tyrosol by horseradish peroxidase (HRP)-H₂O₂ afforded an insoluble product (oligotyrosol, OligoTyr) consisting of mixture of linear oligomers (up to 11-mer) with limited benzylic branching points, as evidenced by ESI-MS and solid state ¹³C NMR analysis. OligoTyr proved to be significantly more active than tyrosol in several antioxidant assays and was not toxic to human osteosarcoma SaOS-2 cells, stimulating alkaline phosphatase (ALP) activity at day 7 in a similar manner as tyrosol. However, when loaded at 5% w/w into highly porous polylactic acid (PLA) scaffolds featuring hierarchical structures, OligoTyr caused a significant increase in the ALP activity of SaOS-2 cells compared to PLA alone, while tyrosol was completely inactive. A release of ca. 5% from PLA was determined after 1 week in a physiological medium. No significant influence on calcium release from PLA scaffolds containing 5% β-tricalcium phosphate was observed.